Each newly designed telecommunication circuit pack has to be tested in a system environment. The system test has to ensure that the behavior of the single circuit pack conforms to the requirements of the system. One kind of these tests is to check if failure, which happened on the circuit pack, will be identified by the application software and correlated into the expected consequent action. Therefore, as an example, SFPs (Small Formfactor Pluggables) have to be removed or disabled. In principle, this has to be done by hand, but from the cost- and time-to-market point of view, this kind of test has to be automated.
A common way of failure simulation in a system environment like optical module (SFP) removal or watchdog disabling is based on separate control lines from a debug or control circuit pack, which is part of the system only during system test. Via the control lines from the debug or control circuit pack, it is possible to stimulate circuit pack failures on each circuit pack at each slots of the system. When one or more of this kind of failure occurs, it will be checked during system test whether the failure has been detected by the system controller entity.
Using the common practice for failure simulation described above, it has the following disadvantages. First, additional control lines have to be designed in the system backplane. Second, the control lines will only be used for system test and are not customer relevant. Third, in order to use those control lines, additional control circuit packs (debug circuit packs) are necessary. Fourth, a test of a fully equipped shelf is not possible, because one slot is always used for the control circuit pack. Fifth, additional failure simulation forced by new circuit pack are often not possible, because new control lines can't be added to an existing backplane.